1. Field of the Invention
This invention relates to an apparatus useful in the formation of sheet material, and more particularly, to an improved die stripping apparatus for use in a can body forming apparatus.
2. Prior Art
It has long been known in the metal forming art that objects may be formed from a metal blank by forcing the blank through a series of ironing dies under the force of a ram. Such a process is used to form the well known one-piece aluminum can body.
Once the can is formed, it is tightly engaged on a punch attached to the end of the ram and must be removed as the ram retracts through the ironing dies.
Strippers are commonly used to remove the formed can from the punch, which strippers usually comprise a plurality of segments that are arranged concentrically about the punch. Typically, the segments are biased against the punch in such a manner so as to move out of the way when the punch is moving downward to form the can, and grip the upper rim of the can when the punch retracts. Such a prior art can stripping apparatus is disclosed in U.S. Pat. No. 4,095,452, which issued to Fred Cruz on June 20, 1978. Other types of can-stripping equipment have been employed in the past, one such can stripper is disclosed in U.S. Pat. No. 3,390,565 of A. Dean Smith, et al. As disclosed, multiple segments of suitable material (e.g. twenty segments of hardened tool steel) are mounted concentrically around a can forming punch. On the final forming action of the punch the can and the punch combination are driven through the stripper section, causing the segments to deflect out of the path of the can and punch. With the passage of the can past the can stripper, the segments return to a position of close proximity to the punch. With the withdrawal of the punch, the segments engage the can opening toward the rear of the punch and hold the can while the punch is further withdrawn, freeing the can from the punch. All of the prior art can strippers work in essentially the same way.
A disadvantage of the prior art can strippers is that due to the combined need for concentricity of the segments with the can punch, and for a depressing movement of the segments, which normally requires some rotation parallel to the longitudinal axis of the punch, the segments must be numerous and relatively small and narrow. This greatly increases the difficulty in adjusting the segments to assure proper engagement with the can without engaging and thereby damaging the punch.
A further disadvantage of the prior art is that the can strippers are relatively complex and expensive.
Another disadvantage of the prior art is that the segments, being small and with little bearing surface, wear rapidly and need relatively frequent replacement.